The present invention relates to a hydrophobic precipitated silica, to a process for the production thereof and to the use thereof.
It is known to hydrophobize precipitated silicas, wherein a wide variety of hydrophobizing agents may be used such as those described in the following: U.S. Pat. No. 3,567,680, DE-AS 24 35 860, GB-A 2 001 303, German patent 15 67 449, DE-AS 11 72 245, DE-B 25 13 608, DE-B 10 74 559, DE-B 12 29 504, EP-A 0 658 523. Thus, the term "hydrophobizing agent" with respect to silica technology is well understood as to its scope and meaning.
Known processes have the disadvantage that two or more stages must sometimes be used, during which the hydrophilic precipitated silica must first be dried and then is not reacted with the silane until a subsequent heat treatment stage; either that or very long reaction times are required despite elevated temperatures.
Moreover, if uniform hydrophobization of the precipitated silica is to be achieved, the precipitated silica must be homogeneously mixed with the silane. However, homogeneous mixing is not possible when an aqueous precipitated silica suspension is used because it is not possible to achieve a homogeneous distribution of the silane due to its hydrophobic properties.
It is therefore an object of the present invention to provide a hydrophobic precipitated silica which does not exhibit these disadvantages.